Liquid supply apparatus and image forming apparatus

ABSTRACT

A liquid supply apparatus includes: a plurality of heat exchange devices which are respectively provided in a plurality of supply paths for supplying liquids to a plurality of liquid ejection heads respectively, are supplied with a liquid medium adjusted to a predetermined temperature from a liquid temperature adjusting device, and conduct heat exchange between the liquids flowing in the plurality of supply paths and the liquid medium supplied from the liquid temperature adjusting device; a plurality of flow rate adjusting devices which are respectively provided correspondingly to the plurality of heat exchange devices and adjust a flow rate of the liquid medium supplied to each of the plurality of heat exchange devices from the liquid temperature adjusting device; and a controller which controls each of the plurality of flow rate adjusting devices to individually change the flow rate of the liquid medium supplied from the liquid temperature adjusting device to the plurality of heat exchange devices.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid supply apparatus and an imageforming apparatus, and more particularly to a technique for performingtemperature control of a liquid supplied to a liquid ejection head.

2. Description of the Related Art

An inkjet recording apparatus is provided with a recording head (inkjethead) in which a plurality of nozzles are arranged in an ejection plane,and an image is formed on a recording medium by ejecting ink dropletsfrom the nozzles, while the recording medium and the recording head aremoved relative to each other. Examples of an ink ejection system of therecording head include a piezoelectric system in which the displacementof a piezoelectric element is used to pressurize the ink inside apressure chamber and eject an ink droplet from the nozzle, and a thermalsystem in which thermal energy generated by a heat-generating elementsuch as a heater is used to generate a gas bubble inside a pressurechamber and eject an ink droplet from the nozzle by the generatedpressure.

Such inkjet recording apparatuses can be of a serial system or a linesystem. The serial system is provided with a recording head in whichnozzle rows are disposed along the conveyance direction of the recordingmedium and recording is performed by repeating intermittently thereciprocating movement of the recording head in the widthwise directionof the recording medium (direction perpendicular to the paper conveyancedirection; main scanning direction) and conveyance of the recordingmedium. The line system is provided with a receding head in which nozzlerows are disposed along the widthwise direction of the recording mediumand recording is performed by moving the recording medium in the paperconveyance direction (sub-scanning direction) with respect to therecording head. One of the benefits of the line system over the serialsystem is in that the recording speed can be increased, and the linesystem can be applied widely to various industrial fields.

An ink supply system (ink supply device) of the inkjet recordingapparatus is provided with an ink tank accommodating ink to be suppliedto the recording head. The ink tank and the recording head are linked byan ink supply path, and a pump serving as a liquid pumping device isinstalled in the ink supply path. The ink is supplied from the ink tankinto the recording head via the ink supply path by driving the pump.

The viscosity of ink used in the inkjet recording apparatus changesaccording to temperature. Therefore, when the temperature of inksupplied to the recording head changes, the ink viscosity changes,thereby causing variations in ink ejection characteristics. For example,when the ink temperature decreases, the ink viscosity increases, causingreduction in the ejection amount or decrease in the flying velocity ofthe ink and creating density unevenness in the recorded image.Accordingly, inkjet recording apparatuses have been heretofore suggestedthat are provided with a temperature adjusting mechanism for adjustingthe temperature of ink supplied to the recording head, with the objectof stabilizing the ejection characteristic of the recording head (see,for example, Japanese Patent Application Publication No. 3-104655).

However, since the inkjet recording apparatus described in JapanesePatent Application Publication No. 3-104655 is provided with atemperature adjusting device for each ink color, the cost of theapparatus is raised. Further, since the total amount of droplets to beejected onto the recording medium is determined, when a temperatureadjusting device is provided for each color, the temperature adjustmentcapability corresponding to the maximum droplet ejection amount isnecessary for each color and an excess capability as a whole isrequired, thereby raising the cost.

In particular, in an inkjet recording apparatus of a line system,increase in the recording speed and increase in quality of recordedimages are required together with wide printing. Therefore, the amountof ink consumed by the recording head (ejection amount) is increased andthe amount of generated heat also increases due to increase in a drivefrequency. Further, since accuracy needed for ink temperature rises, acontrollable temperature range of ink is narrowed.

Thus, a strong temperature adjustment capability is needed for the inksupplied to the recording head and a stringent requirement is alsoplaced on control accuracy relating to ink temperature adjustment. Theproblem is that these requirements cannot be met by the temperatureadjustment performed by air cooling, such as used in the inkjetrecording apparatus described in Japanese Patent Application PublicationNo. 3-104655.

Using a water cooling system to adjust the temperature of ink suppliedto the recording head can be also considered, but this approach couldresult in undesirable significant cost increase because the inktemperature is adjusted separately for each recording head.

SUMMARY OF THE INVENTION

The present invention has been conceived with the foregoing in view andit is an object of the present invention to provide a liquid supplyapparatus and an image forming apparatus that can adjust the temperatureof liquid supplied to a liquid ejection head and stabilize the ejectionof the liquid ejection head, without increasing the cost significantly.

In order to attain an object described above, one aspect of the presentinvention is directed to a liquid supply apparatus comprising: aplurality of heat exchange devices which are respectively provided in aplurality of supply paths for supplying liquids to a plurality of liquidejection heads respectively, are supplied with a liquid medium adjustedto a predetermined temperature from a liquid temperature adjustingdevice, and conduct heat exchange between the liquids flowing in theplurality of supply paths and the liquid medium supplied from the liquidtemperature adjusting device; a plurality of flow rate adjusting deviceswhich are respectively provided correspondingly to the plurality of heatexchange devices and adjust a flow rate of the liquid medium supplied toeach of the plurality of heat exchange devices from the liquidtemperature adjusting device; and a controller which controls each ofthe plurality of flow rate adjusting devices to individually change theflow rate of the liquid medium supplied from the liquid temperatureadjusting device to the plurality of heat exchange devices.

According to this aspect of the invention, by controlling each of theflow rate control valves provided respectively between the liquidtemperature adjusting device and the heat exchange units, the suppliedamount of liquid medium that is supplied to each heat exchange unit canbe individually changed and the heat exchange ratio of liquid (ink) andliquid medium in each heat exchange unit can be varied for each heatexchange unit. As a result, the temperature of liquid supplied to eachliquid ejection head can be individually adjusted, ejection stability ofeach liquid ejection head can be stabilized, and inconveniences such asdensity unevenness caused by the difference in liquid temperature can beeliminated. Further, since the temperature of liquid supplied to eachliquid ejection head can be adjusted for each type of liquid (forexample, for each color of liquid) only by changing the supplied amountof liquid medium supplied to each heat exchange unit, no excesstemperature adjustment capability is required for each type of liquidand cost can be reduced.

Desirably, the plurality of flow rate adjusting devices are flow ratecontrol valves; and the controller changes opening area of the flow ratecontrol valves to change the flow rate of the liquid medium suppliedfrom the liquid temperature adjusting device to the plurality of heatexchange devices.

According to this aspect of the invention, the flow rate of liquidmedium supplied to each heat exchange unit can be finely adjusted foreach heat exchange unit and the temperature of liquid supplied to eachliquid ejection head can be optimized.

Desirably, each of the plurality of flow rate adjusting devices includesa plurality of parallel flow paths in parallel connected in anindividual flow path of the liquid medium to the heat exchange device,and a plurality of electromagnetic valves respectively provided in theplurality of parallel flow paths; and the controller controls openingand closing of the plurality of electromagnetic valves to change theflow rate of the liquid medium supplied from the liquid temperatureadjusting device to the plurality of heat exchange devices.

According to this aspect of the invention, the flow rate of liquidsupplied to each heat exchange unit can be adjusted by controllingtogether the opening and closing of electromagnetic valves provided ineach parallel flow path. Further, by using electromagnetic valves thatare cheaper and easier to control than flow rate control valves, it ispossible to reduce the cost of the liquid supply apparatus.

Desirably, part or all of the plurality of parallel flow paths havemutually different flow path resistances.

According to this aspect of the invention, the adjustment range of theflow rate of liquid supplied to each heat exchange unit can bebroadened.

Desirably, all of the plurality of parallel flow paths have a same flowpath resistance.

According to this aspect of the invention, since the flow rate of liquidsupplied to a heat exchange units is proportional to the number ofparallel flow paths in which electromagnetic valves are open, from amongthe plurality of parallel flow paths corresponding to the heat exchangeunit, the flow rate control performed by the controller can besimplified.

Desirably, the liquid supply apparatus further comprises a plurality ofliquid temperature measuring devices which measure temperature of theliquids supplied to the plurality of liquid ejection heads respectively,wherein the controller controls each of the plurality of flow rateadjusting devices according to the temperature of the liquids measuredby the plurality of liquid temperature measuring devices.

According to this aspect of the invention, by adjusting the flow rate ofliquid medium supplied to the heat exchange units correspondingly to thetemperature of liquid inside the liquid ejection heads, it is possibleto set the liquid inside the liquid ejection heads to desiredtemperature.

Desirably, the liquid supply apparatus further comprises a plurality ofliquid flow rate measuring devices which measure flow rates of theliquids supplied to the plurality of liquid ejection heads respectively,wherein the controller controls each of the plurality of flow rateadjusting devices according to the flow rates of the liquids measured bythe plurality of liquid flow rate measuring devices.

In this aspect of the invention, the liquid flow rate measuring devicesmay be flow rate sensors provided in supply paths for supplying theliquid to the liquid ejection heads, or may be revolution speed sensorsthat detect the revolution speed of pumps provided as liquid pumpingdevices in the supply paths.

Desirably, the liquid supply apparatus further comprises a head ejectionratio calculation device which calculates ejection ratios of theplurality of liquid ejection heads,

wherein the controller controls the plurality of flow rate adjustingdevices according to the ejection ratios of the plurality of liquidejection heads calculated by the head ejection ratio calculation device.

In this aspect of the invention, the flow rate of liquid medium suppliedto the heat exchange units is desirably adjusted according to theejection ratios of the liquid ejection heads. There is a correlationbetween the ejection ratio of the liquid ejection head and thetemperature of liquid inside thereof, and by adjusting the flow rate ofliquid medium supplied to the heat exchange units on the basis of theejection ratios of the liquid ejection heads, it is possible to set theliquid inside the liquid ejection heads to desired temperature.

Desirably, the controller controls each of the plurality of flow rateadjusting devices and also controls temperature of the liquid mediumadjusted by the liquid temperature adjusting device.

According to this aspect of the invention, the temperature of liquidsupplied to each liquid ejection head can be further optimized.

In order to attain an object described above, another aspect of thepresent invention is directed to an image forming apparatus comprisingany one of the liquid supply apparatuses above.

According to the present invention, by controlling each of the flow ratecontrol valves provided between the liquid temperature adjusting deviceand heat exchange units, the supplied amount of liquid medium that issupplied to each heat exchange unit can be individually changed and theheat exchange ratio of ink and liquid medium in each heat exchange unitcan be varied for each heat exchange unit. As a result, the temperatureof liquid supplied to each liquid ejection head can be individuallyadjusted, ejection stability of each liquid ejection head can bestabilized, and inconveniences such as density unevenness caused by thedifference in liquid temperature can be eliminated. Further, since thetemperature of liquid supplied to each liquid ejection head can beadjusted for each type of liquid (for example, for each color of liquid)by changing the supplied amount of liquid medium supplied to each heatexchange unit, no excess temperature adjustment capability is requiredfor each type of liquid and cost can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The nature of this invention, as well as other objects and benefitsthereof, will be explained in the following with reference to theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures and wherein:

FIG. 1 is a general configuration drawing illustrating schematically aninkjet recording apparatus;

FIG. 2 is a principal plan view illustrating a printing unit peripheryof the inkjet recording apparatus;

FIGS. 3A to 3C are plan transparent views illustrating examples of headstructure;

FIG. 4 is a cross-sectional view illustrating an ink chamber unit;

FIG. 5 is a principal block diagram illustrating a control system of theinkjet recording apparatus;

FIG. 6 is a schematic drawing illustrating a configuration example of anink supply system according to a first embodiment;

FIG. 7 is a graph showing an example of relationship between the coolingwater flow rate and warm water outlet temperature;

FIG. 8 is a schematic diagram illustrating another configuration exampleof an ink supply system according to the first embodiment;

FIG. 9 is a schematic diagram illustrating yet another configurationexample of the ink supply system according to the first embodiment, and

FIG. 10 is a schematic diagram illustrating a configuration example ofan ink supply system according to a second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS General Configuration of InkjetRecording Apparatus

FIG. 1 is a general schematic configuration diagram of an inkjetrecording apparatus according to an embodiment of an image formingapparatus of the present invention. As illustrated in FIG. 1, the inkjetrecording apparatus 10 comprises: a printing unit 12 having a pluralityof recording heads (hereafter, also simply called “heads”) 50K, 50C,50M, and 50Y provided for the respective ink colors; an ink storing andloading unit 14 for storing inks of K, C, M and Y to be supplied to theprinting heads 50K, 50C, 50M, and 50Y; a paper supply unit 18 forsupplying recording paper 16; a decurling unit 20 removing curl in therecording paper 16; a suction belt conveyance unit 22 disposed facingthe nozzle face (ink-droplet ejection face) of the printing unit 12, forconveying the recording paper 16 while keeping the recording paper 16flat; a print determination unit 24 for reading the printed resultproduced by the printing unit 12; and a paper output unit 26 foroutputting image-printed paper (printed matter) to the exterior.

In FIG. 1, a magazine for rolled paper (continuous paper) is shown as anexample of the paper supply unit 18; however, more magazines with paperdifferences such as paper width and quality may be jointly provided.Moreover, papers may be supplied with cassettes that contain cut papersloaded in layers and that are used jointly or in lieu of the magazinefor rolled paper.

In the case of the configuration in which roll paper is used, a cutter28 is provided as illustrated in FIG. 1, and the continuous paper is cutinto a desired size by the cutter 28. The cutter 28 has a stationaryblade 28A, whose length is not less than the width of the conveyorpathway of the recording paper 16, and a round blade 28B, which movesalong the stationary blade 28A. The stationary blade 28A is disposed onthe reverse side of the printed surface of the recording paper 16, andthe round blade 28B is disposed on the printed surface side across theconveyor pathway. When cut papers are used, the cutter 28 is notrequired.

In the case of a configuration in which a plurality of types ofrecording paper can be used, it is desirable that an informationrecording medium such as a bar code and a wireless tag containinginformation about the type of paper is attached to the magazine, and byreading the information contained in the information recording mediumwith a predetermined reading device, the type of paper to be used isautomatically determined, and ink-droplet ejection is controlled so thatthe ink-droplets are ejected in an appropriate manner in accordance withthe type of paper.

The recording paper 16 delivered from the paper supply unit 18 retainscurl due to having been loaded in the magazine. In order to remove thecurl, heat is applied to the recording paper 16 in the decurling unit 20by a heating drum 30 in the direction opposite from the curl directionin the magazine. The heating temperature at this time is desirablycontrolled so that the recording paper 16 has a curl in which thesurface on which the print is to be made is slightly round outward.

The decurled and cut recording paper 16 is delivered to the suction beltconveyance unit 22. The suction belt conveyance unit 22 has aconfiguration in which an endless belt 33 is set around rollers 31 and32 so that the portion of the endless belt 33 facing at least the nozzleface of the printing unit 12 and the sensor face of the printdetermination unit 24 forms a plane.

The belt 33 has a width that is greater than the width of the recordingpaper 16, and a plurality of suction apertures (not shown) are formed onthe belt surface. A suction chamber 34 is disposed in a position facingthe sensor surface of the print determination unit 24 and the nozzlesurface of the printing unit 12 on the interior side of the belt 33,which is set around the rollers 31 and 32, as illustrated in FIG. 1. Thesuction chamber 34 provides suction with a fan 35 to generate a negativepressure, and the recording paper 16 on the belt 33 is held by suction.

The belt 33 is driven in the clockwise direction in FIG. 1 by the motiveforce of a motor (not shown) being transmitted to at least one of therollers 31 and 32, which the belt 33 is set around, and the recordingpaper 16 held on the belt 33 is conveyed from left to right in FIG. 1.

Since ink adheres to the belt 33 when a marginless print job or the likeis performed, a belt-cleaning unit 36 is disposed in a predeterminedposition (a suitable position outside the printing area) on the exteriorside of the belt 33. Although the details of the configuration of thebelt-cleaning unit 36 are not shown, examples thereof include aconfiguration in which the belt 33 is nipped with cleaning rollers suchas a brush roller and a water absorbent roller, an air blowconfiguration in which clean air is blown onto the belt 33, and acombination of these. In the case of the configuration in which the belt33 is nipped with the cleaning rollers, it is desirable to make the linevelocity of the cleaning rollers different from that of the belt 33 toimprove the cleaning effect.

A roller nip conveyance mechanism, in place of the suction beltconveyance unit 22, can be employed. However, there is a drawback in theroller nip conveyance mechanism that the print tends to be smeared whenthe printing area is conveyed by the roller nip action because the niproller makes contact with the printed surface of the paper immediatelyafter printing. Therefore, the suction belt conveyance in which nothingcomes into contact with the image surface in the printing area isdesirable.

A heating fan 40 is disposed on the upstream side of the printing unit12 in the conveyance pathway formed by the suction belt conveyance unit22. The heating fan 40 blows heated air onto the recording paper 16 toheat the recording paper 16 immediately before printing so that the inkdeposited on the recording paper 16 dries more easily.

The printing unit 12 is a so-called “full line head” in which a linehead having a length corresponding to the maximum paper width isarranged in a direction (main scanning direction) that is perpendicularto the paper conveyance direction (sub scanning direction). Each of theprinting heads 50K, 50C, 50M, and 50Y constituting the printing unit 12is constituted by a line head, in which a plurality of ink ejectionports (nozzles) are arranged along a length that exceeds at least oneside of the maximum-size recording paper 16 intended for use in theinkjet recording apparatus 10 (see FIG. 2).

The printing heads 50K, 50C, 50M, and 50Y are arranged in the order ofblack (K), cyan (C), magenta (M), and yellow (Y) from the upstream side,along the feed direction of the recording paper 16 (hereinafter,referred to as the sub-scanning direction). A color image can be formedon the recording paper 16 by ejecting the inks from the printing heads50K, 50C, 50M, and 50Y, respectively, onto the recording paper 16 whileconveying the recording paper 16.

By adopting the printing unit 12 in which the full line heads coveringthe full paper width are provided for the respective ink colors in thisway, it is possible to record an image on the full surface of therecording paper 16 by performing just one operation of relatively movingthe recording paper 16 and the printing unit 12 in the paper conveyancedirection (the sub-scanning direction), in other words, by means of asingle sub-scanning action. Higher-speed printing is thereby madepossible and productivity can be improved in comparison with a shuttletype head configuration in which a head reciprocates in a direction (themain scanning direction) orthogonal to the paper conveyance direction.

Although the configuration with the KCMY four standard colors isdescribed in the present embodiment, combinations of the ink colors andthe number of colors are not limited to those. Light inks or dark inkscan be added as required. For example, a configuration is possible inwhich heads for ejecting light-colored inks such as light cyan and lightmagenta are added. Furthermore, there are no particular restrictions ofthe sequence in which the heads of respective colors are arranged.

As illustrated in FIG. 1, the ink storing and loading unit 14 has tanksfor storing the inks of K, C, M and Y to be supplied to the heads 50K,50C, 50M, and 50Y, and the tanks are connected to the heads 50K, 50C,50M, and 50Y by means of channels, which are omitted from figures. Theink storing and loading unit 14 has a warning device (for example, adisplay device or an alarm sound generator) for warning when theremaining amount of any ink is low, and has a mechanism for preventingloading errors among the colors.

The print determination unit 24 has an image sensor (line sensor) forcapturing an image of the ink-droplet deposition result of the printingunit 12, and functions as a device to check for ejection defects such asclogs of the nozzles in the printing unit 12 from the ink-dropletdeposition results evaluated by the image sensor.

The print determination unit 24 of the present embodiment is configuredwith at least a line sensor having rows of photoelectric transducingelements with a width that is greater than the ink-droplet ejectionwidth (image recording width) of the heads 50K, 50C, 50M, and 50Y. Thisline sensor has a color separation line CCD sensor including a red (R)sensor row composed of photoelectric transducing elements (pixels)arranged in a line provided with an R filter, a green (G) sensor rowwith a G filter, and a blue (B) sensor row with a B filter. Instead of aline sensor, it is possible to use an area sensor composed ofphotoelectric transducing elements which are arranged two-dimensionally.

The print determination unit 24 reads a test pattern image printed bythe heads 50K, 50C, 50M, and 50Y for the respective colors, and theejection of each head is determined. The ejection determination includesmeasurement of the presence of the ejection, measurement of the dotsize, and measurement of the dot deposition position.

A post-drying unit 42 is disposed following the print determination unit24. The post-drying unit 42 is a device to dry the printed imagesurface, and includes a heating fan, for example. It is desirable toavoid contact with the printed surface until the printed ink dries, anda device that blows heated air onto the printed surface is desirable.

In cases in which printing is performed with dye-based ink on porouspaper, blocking the pores of the paper by the application of pressureprevents the ink from coming contact with ozone and other substancesthat cause dye molecules to break down, and has the effect of increasingthe durability of the print.

A heating/pressurizing unit 44 is disposed following the post-dryingunit 42. The heating/pressurizing unit 44 is a device to control theglossiness of the image surface, and the image surface is pressed with apressure roller 45 having a predetermined uneven surface shape while theimage surface is heated, and the uneven shape is transferred to theimage surface.

The printed matter generated in this manner is outputted from the paperoutput unit 26. The target print (i.e., the result of printing thetarget image) and the test print are desirably outputted separately. Inthe inkjet recording apparatus 10, a sorting device (not shown) isprovided for switching the outputting pathways in order to sort theprinted matter with the target print and the printed matter with thetest print, and to send them to paper output units 26A and 26B,respectively. When the target print and the test print aresimultaneously formed in parallel on the same large sheet of paper, thetest print portion is cut and separated by a cutter (second cutter) 48.The cutter 48 is disposed directly in front of the paper output unit 26,and is used for cutting the test print portion from the target printportion when a test print has been performed in the blank portion of thetarget print. The structure of the cutter 48 is the same as the firstcutter 28 described above, and has a stationary blade 48A and a roundblade 48B.

Although not illustrated in FIG. 1, the paper output unit 26A for thetarget prints is provided with a sorter for collecting prints accordingto print orders.

Structure of Head

Next, the structure of heads 50K, 50C, 50M, and 50Y will be described.The heads 50K, 50C, 50M, and 50Y of the respective ink colors have thesame structure, and a reference numeral 50 is hereinafter designated toany of the heads.

FIG. 3A is a plan perspective diagram showing an example of thestructure of a head 50, and FIG. 3B is a partial enlarged diagram ofsame. Moreover, FIG. 3C is a plan view perspective diagram showing afurther example of the structure of the head 50. FIG. 4 is across-sectional diagram showing the composition of an ink chamber unit(a cross-sectional diagram along line IV-IV in FIGS. 3A and 3B).

The nozzle pitch in the head 50 should be minimized in order to maximizethe density of the dots formed on the surface of the recording paper. Asillustrated in FIGS. 3A and 3B, the head 50 according to the presentembodiment has a structure in which a plurality of ink chamber units 53,each comprising a nozzle 51 forming an ink droplet ejection hole, apressure chamber 52 corresponding to the nozzle 51, and the like, aredisposed two-dimensionally in the form of a staggered matrix, and hencethe effective nozzle interval (the projected nozzle pitch) as projectedin the lengthwise direction of the head (the main scanning directionperpendicular to the paper conveyance direction) is reduced and highnozzle density is achieved.

The mode of forming one or more nozzle rows through a lengthcorresponding to the entire width of the recording paper 16 in adirection substantially perpendicular to the paper conveyance directionis not limited to the example described above. For example, instead ofthe configuration in FIG. 3A, as illustrated in FIG. 3C, a line headhaving nozzle rows of a length corresponding to the entire width of therecording paper 16 can be formed by arranging and combining, in astaggered matrix, short modules (head chips) 50′ having a plurality ofnozzles 51 arrayed in a two-dimensional fashion. Furthermore, althoughnot shown in the drawings, it is also possible to compose a line head byarranging short heads in one row.

The pressure chambers 52 provided corresponding to the respectivenozzles 51 are approximately square-shaped in planar form, and a nozzle51 and an ink inflow port 54 are provided respectively at either cornerof a diagonal of each pressure chamber 52. Each pressure chamber 52 isconnected via the ink inflow port 54 to a common flow channel 55.

Piezoelectric elements 58 respectively provided with individualelectrodes 57 are bonded to a diaphragm 56 which forms the upper face ofthe pressure chambers 52 and also serves as a common electrode, and eachpiezoelectric element 58 is deformed when a drive voltage is supplied tothe corresponding individual electrode 57, thereby causing ink to beejected from the corresponding nozzle 51. When ink is ejected, new inkis supplied to the pressure chambers 52 from the common flow channel 55,via the ink inlet ports 54.

In the present example, a piezoelectric element 58 is used as an inkejection force generating device which causes ink to be ejected from anozzle 50 provided in a head 51, but it is also possible to employ athermal method in which a heater is provided inside the pressure chamber52 and ink is ejected by using the pressure of the film boiling actioncaused by the heating action of this heater.

As illustrated in FIG. 3B, the high-density nozzle head according to thepresent embodiment is achieved by arranging a plurality of ink chamberunits 53 having the above-described structure in a lattice fashion basedon a fixed arrangement pattern, in a row direction which coincides withthe main scanning direction, and a column direction which is inclined ata fixed angle of θ with respect to the main scanning direction, ratherthan being perpendicular to the main scanning direction.

More specifically, by adopting a structure in which a plurality of inkchamber units 53 are arranged at a uniform pitch d in line with adirection forming an angle of θ with respect to the main scanningdirection, the pitch P of the nozzles projected so as to align in themain scanning direction is d×cos θ, and hence the nozzles 51 can beregarded to be equivalent to those arranged linearly at a fixed pitch Palong the main scanning direction. Such configuration results in anozzle structure in which the nozzle row projected in the main scanningdirection has a high nozzle density of up to 2,400 nozzles per inch.

When implementing the present invention, the arrangement structure ofthe nozzles is not limited to the example shown in the drawings, and itis also possible to apply various other types of nozzle arrangements,such as an arrangement structure having one nozzle row in thesub-scanning direction.

Furthermore, the scope of application of the present invention is notlimited to a printing system based on a line type of head, and it isalso possible to adopt a serial system where a short head which isshorter than the breadthways dimension of the recording paper 16 isscanned in the breadthways direction (main scanning direction) of therecording paper 16, thereby performing printing in the breadthwaysdirection, and when one printing action in the breadthways direction hasbeen completed, the recording paper 16 is moved through a prescribedamount in the direction perpendicular to the breadthways direction (thesub-scanning direction), printing in the breadthways direction of therecording paper 16 is carried out in the next printing region, and byrepeating this sequence, printing is performed over the whole surface ofthe printing region of the recording paper 16.

Configuration of Control System

FIG. 5 is a principal block diagram showing the control system of theinkjet recording apparatus 10. The inkjet recording apparatus 10comprises a communications interface 70, a system controller 72, amemory 74, a motor driver 76, a heater driver 78, a print control unit80, an image buffer memory 82, a head driver 84, a liquid temperaturecontrol unit 96, a valve control unit 98, and the like.

The communications interface 70 is an interface unit for receiving imagedata sent from a host computer 86. A serial interface such as USB(Universal Serial Bus), IEEE1394, Ethernet (registered trademark),wireless network, or a parallel interface such as a Centronics interfacemay be used as the communications interface 70. A buffer memory (notshown) may be mounted in this portion in order to increase thecommunication speed.

The image data sent from the host computer 86 is received by the inkjetrecording apparatus 10 through the communications interface 70, and istemporarily stored in the memory 74. The memory 74 is a storage devicefor temporarily storing images inputted through the communicationsinterface 70, and data is written and read to and from the memory 74through the system controller 72. The memory 74 is not limited to amemory composed of semiconductor elements, and a hard disk drive oranother magnetic medium may be used.

The system controller 72 is a control unit which controls the respectivesections, such as the communications interface 70, the memory 74, themotor driver 76, the heater driver 78, the pump driver 92, the liquidtemperature control unit 96, the valve control unit 98, and the like.The system controller 72 is made up of a central processing unit (CPU)and peripheral circuits thereof, and as well as controllingcommunications with the host computer 86 and controlling reading fromand writing to the memory 74, and the like, and it generates controlsignals for controlling the motors 88 of the conveyance system and theheaters 89.

Programs executed by the CPU of the system controller 72 and the varioustypes of data which are required for control procedures are stored inthe memory 74. The memory 74 may be a non-writeable storage device, orit may be a rewriteable storage device, such as an EEPROM. The memory 74is used as a temporary storage region for the image data, and it is alsoused as a program development region and a calculation work region forthe CPU.

Various control programs are stored in the program storage unit 90, andthe control programs are read and executed in response to indications ofthe system controller 72. The program storage unit 90 may use asemiconductor memory such as ROM or an EEPROM, or may use a magneticdisk or the like. An external interface may be provided and a memorycard or a PC card may be used. It goes without saying that a pluralityof recording media may be selected from among these recording media. Theprogram storage unit 90 may be also used together with a storage device(not shown in the figure) of an operation parameter or the like.

The motor driver (drive circuit) 76 drives the motor 88 in accordancewith commands from the system controller 72. The heater driver 78 drivesthe heater 89 of the post-drying unit 42 and the like in accordance withcommands from the system controller 72.

The pump driver 92 is a driver that drives the pump 94 according to aninstruction from the system controller 72. The pump 94 shown in FIG. 5includes pumps (for example, a pump 102 in FIG. 6) disposed in the inksupply system of the inkjet recording apparatus 10.

The liquid temperature control unit 96 is a control unit that controlsthe temperature of liquid medium (cooling water) of the liquidtemperature adjusting device 106 according to an instruction from thesystem controller 72. As will be described below, the liquid temperatureadjusting device 106 is provided as a device shared by all colors,rather than for each ink color, and the liquid medium adjusted to thepredetermined temperature by the liquid temperature adjusting device 106circulates in the heat exchange units 104 (see FIG. 6) providedrespectively for the colors.

The valve control unit 98 controls the valve 99 according to aninstruction from the system controller 72. The valve 99 shown in FIG. 5includes the flow rate control valve 108 shown in FIG. 6 and theelectromagnetic valve 132 shown in FIG. 10.

The print control unit 80 has a signal processing function forperforming various tasks, compensations, and other types of processingfor generating print control signals from the image data stored in thememory 74 in accordance with commands from the system controller 72 soas to supply the generated print control signals (dot data) to the headdriver 84. Necessary signal processing is carried out in the printcontrol unit 80, and the ejection amount and the ejection timing of theink from the respective recording heads 50 are controlled via the headdriver 84, on the basis of the print data. By this means, desired dotsize and dot positions can be achieved.

The print control unit 80 is provided with the image buffer memory 82;and image data, parameters, and other data are temporarily stored in theimage buffer memory 82 when image data is processed in the print controlunit 80. The aspect illustrated in FIG. 5 is one in which the imagebuffer memory 82 accompanies the print control unit 80; however, thememory 74 may also serve as the image buffer memory 82. Also possible isan aspect in which the print control unit 80 and the system controller72 are integrated to form a single processor.

The head driver 84 generates drive signals for driving the piezoelectricelements 58 (see FIG. 4) of the recording heads 50 of the respectivecolors, on the basis of dot data supplied from the print control unit80, and supplies the generated drive signals to the piezoelectricelements 58. A feedback control system for maintaining constant driveconditions in the recording heads 50 may be included in the head driver84.

The print determination unit 24 is a block that includes the line sensoras described above with reference to FIG. 1, reads the image printed onthe recording paper 16, determines the print conditions (presence of theejection, variation in the dot formation, and the like) by performingprescribed signal processing, and the like, and provides thedetermination results of the print conditions to the print control unit80.

According to requirements, the print control unit 80 makes variouscorrections with respect to the recording head 50 on the basis ofinformation obtained from the print determination unit 24.

Configuration of Ink Supply System

Configuration examples (first and second embodiments) of ink supplysystem (ink supply device) of the inkjet recording apparatus 10, whichis a specific component in accordance with the present invention, willbe explained below. The reference numerals of components provided foreach color will be assigned at the right end thereof with an alphabetletter (C/M/Y/K) indicating each color, but when the explanation isgiven without distinguishing the colors, the alphabet letter and theright end of reference numeral will be omitted.

First Embodiment

FIG. 6 is a schematic drawing illustrating a configuration example ofink supply system according to a first embodiment. As shown in FIG. 6,the ink supply system according to the first embodiment is constitutedmainly by a head 50, a liquid storage unit 100, a pump 102, and a heatexchange unit 104 for each ink color.

The ink storage unit 100 is a basic tank (ink supply source)accommodating ink for supply to each corresponding head 50 andcorresponds to a tank disposed in the ink storage/loading unit 14 shownin FIG. 1.

The pump 102 is a pumping device installed between the liquid storageunit 100 and the head 50. By driving the pump 102, the ink is suppliedfrom the liquid storage unit 100 to the head 50. In the configurationshown by way of the example in FIG. 6, the pump 102 is installed betweenthe heat exchange unit 104 and the head 50, but this configuration isnot limiting, and the pump 102 may be also installed between the liquidstorage unit 100 and the heat exchange unit 104.

The heat exchange unit 104 is a heat exchange device installed betweenthe liquid storage unit 100 and the head 50. The liquid medium (coolingwater) supplied from the below-described liquid temperature adjustingdevice 106 is circulated in the heat exchange unit 104, and when the inkis supplied from the liquid storage unit 100 to the head 50, thetemperature of ink passing through the heat exchange unit 104 isadjusted by heat exchange with the liquid medium.

The liquid temperature adjusting device (chiller) 106 is a device thatcauses the liquid medium (cooling water) adjusted to the predeterminedtemperature to circulate between the liquid temperature adjusting device106 and each heat exchange unit 104. The liquid medium adjusted to thepredetermined temperature in the liquid temperature adjusting device 106is supplied to each heat exchange unit 104 via a plurality of firstbranch flow paths 116 which branch off from one supply flow path 114.The liquid medium that has circulated inside the heat exchange units 104and has been discharged is returned from second branch flow paths 118respectively connected to the heat exchange units 104 to the liquidtemperature adjusting device 106 via a single merged recovery flow path120. The liquid temperature adjusting device 106 incorporates a pump(not shown in the figures) as a pumping device for causing the liquidmedium to circulate between the liquid temperature adjusting device 106and the heat exchange units 104. The pump can be also provided outsidethe liquid temperature adjusting device 106.

Respective flow rate control valves 108 are provided between the liquidtemperature adjusting device 106 and the heat exchange units 104. Theflow rate control valves 108 are flow rate adjusting devices that adjustthe supplied amount (circulated amount) of liquid medium (cooling water)supplied from the liquid temperature adjusting device 106 to the heatexchange units 104. The flow rate control valves 108 are controlled bythe below-described controller 112.

Each head 50 is provided with a temperature sensor 110. The temperaturesensor 110 is an ink temperature measuring device that measures thetemperature of ink inside the head 50. The controller 112 is notified ofthe ink temperature (measured value) measured by the temperature sensor110. The temperature sensor 110 may measure not only the temperature ofink inside the head 50, but also the temperature of ink flowing in aflow path connected to the head 50.

The controller 112 changes the opening area (opening ratio) of thecorresponding flow rate control valve 108 on the basis of inktemperature sent from each temperature sensor 110, so as to control thesupplied amount (circulated amount) of liquid medium supplied from theliquid temperature adjusting device 106 to each heat exchange unit 104.The controller 112 is a controller corresponding to the systemcontroller 72 and valve control unit 98 shown in FIG. 5.

FIG. 7 shows how the ink outlet temperature (outlet temperature of inkflowing out from the heat exchange unit 104) varies when the coolingwater flow rate is changed in the case in which cooling water is used asthe liquid medium. The graph in FIG. 7 shows the relationship betweenthe cooling water flow rate and the ink outlet temperature when the inkinlet temperature (inlet temperature of ink flowing into the heatexchange unit 104) is taken as 64° C. and the cooling water inlettemperature (temperature of cooling water supplied to the heat exchangeunit 104) is taken as 18° C. As indicated in this graph, when thecooling water flow rate is increased, the heat exchange ratio in theheat exchange unit 104 rises, the ink can be better cooled by the heatexchange unit 104 and the ink outlet temperature can be lowered.

Accordingly, with the controller 112 of the present embodiment, when thetemperature of ink inside the head 50 is higher than a reference value,the flow rate control valve 108 is controlled so as to increase the flowrate of liquid medium circulating in the heat exchange unit 104. As aresult, the heat exchange ratio in the heat exchange unit 104 can beraised and the temperature of ink supplied to the head 50 (outlettemperature of ink flowing out from the heat exchange unit 104) can belowered.

When the temperature of ink inside the head 50 is lower than thereference value, the controller 112 controls the flow rate control valve108 so as to reduce the flow rate of liquid medium circulating in theheat exchange unit 104. As a result, the heat exchange ratio in the heatexchange unit 104 can be reduced and the temperature of ink supplied tothe head 50 can be raised.

The configuration example shown in FIG. 6 relates to a feedback controlsystem in which a difference between the temperature of ink supplied tothe head 50 and the reference value (reference temperature) is reflectedin the opening ratio of the flow rate control valve 108.

Instead of the configuration example shown in FIG. 6, it is possible tomaintain a table indicating the relationship between the temperature ofink supplied to the head 50 and the opening ratio of the flow ratecontrol valve 108, and apply feedforward control that determines theopening ratio of the flow rate control valve 108 correspondingly to theink temperature.

A specific example will be described below. For example, when a solidimage of cyan color is formed, only a head 50C corresponding to the inkof cyan color, from among the plurality of heads 50C, 50M, 50Y, 50K,generates heat and therefore the temperature of ink inside the head 50Crises. In such a case, the opening area (opening degree) of the flowrate control valve 108C corresponding to the head 50C is increased, thesupplied amount of liquid medium supplied to the heat exchange unit 104Cis raised in such a manner that the heat exchange ratio (temperatureadjustment efficiency) of the heat exchange unit 104C is increased.

Further, when a black text image is formed, only a head 50Kcorresponding to the ink of black color, from among the plurality ofheads 50C, 50M, 50Y, 50K, generates heat and therefore the temperatureof ink inside the head 50K rises. In such a case, the opening area(opening degree) of the flow rate control valve 108K corresponding tothe head 50K is increased, the supplied amount of liquid medium suppliedto the heat exchange unit 104C is raised and the heat exchange ratio(temperature adjustment efficiency) of the heat exchange unit 104C isincreased. The increase in the opening area (opening degree) of the flowrate control valve 108 may not be as large as in the case in which theaforementioned solid image is formed.

When a diagram (graphic) composed of a plurality of colors is formed,one or a plurality of heads 50 corresponding to colors with a highejection ratio, from among the plurality of heads 50C, 50M, 50Y, 50K,generates heat. Therefore, the opening area (opening degree) of the flowrate control valve 108 corresponding to the head 50 with a high ejectionratio is increased, the supplied amount of liquid medium supplied to thecorresponding heat exchange unit 104 is raised and the heat exchangeratio (temperature adjustment efficiency) of the heat exchange unit 104is increased.

Thus, according to the first embodiment, by controlling each flow ratecontrol valve 108 provided between the liquid temperature adjustingdevice 106 and the heat exchange units 104, it is possible to changeindividually the supplied amount (circulated amount) of liquid mediumsupplied to each heat exchange unit 104 and vary the heat exchange ratiobetween the ink and liquid medium in each heat exchange unit 104 withrespect to each heat exchange unit 104 (that is, with respect to eachink color). As a result, the temperature of ink supplied to the head 50corresponding to each color can be individually adjusted, ejection ofeach head 50 can be stabilized, and inconveniences such as densityunevenness caused by the difference in ink temperature can beeliminated.

Further, since the temperature of ink supplied to each head 50 can beadjusted for each ink color (each head) only by changing the suppliedamount of liquid medium supplied to each heat exchange unit 104, noexcess temperature adjustment capability is required for each ink colorand cost can be reduced.

Further, in the present embodiment, the feedback control systemconfiguration is shown in which the flow rate control valve 108 iscontrolled on the basis of ink temperature inside the head 50, but sucha configuration is not limiting, and a configuration of feedback controlsystem conducting control on the basis of ink amount (flow rate)supplied to the head 50 or ejection ratio of the head 50 is alsobeneficial.

FIG. 8 is a schematic diagram illustrating another configuration exampleof ink supply system according to the first embodiment. In FIG. 8,components common or analogous to those shown in FIG. 6 are assignedwith like numeral symbols and explanation thereof is omitted.

The configuration shown in FIG. 8 is provided with a plurality ofrevolution speed sensors 122 (122K, 122C, 122M, 122Y) that determinerevolution speed of the pumps 102 respectively. Each revolution speedsensor 122 detects the revolution speed of the corresponding pump 102,and notifies the controller 112 of the detection result. The controller112 controls the corresponding flow rate control valve 108 on the basisof the detected value (revolution speed of the pump 102) received fromeach revolution speed sensor 122.

For example, when the revolution speed of the pump 102 detected by therevolution speed sensor 122 is lower than a reference value, thesupplied amount of ink supplied to the head 50 is small, the heatexchange efficiency in the heat exchange unit 104 rises, and thetemperature of ink supplied to the head 50 tends to decrease. Therefore,the controller 112 controls the flow rate control valve 108 so that theflow rate of liquid medium circulating in the heat exchange unit 104decreases. As a result, the heat exchange efficiency (heat exchangerate) in the heat exchange unit 104 decreases, the temperature of inksupplied to the head 50 rises, and the ink temperature inside the head50 gradually approaches the reference value.

When the revolution speed of the pump 102 detected by the revolutionspeed sensor 122 is higher than the reference value, the supplied amountof ink supplied to the head 50 is large, the heat exchange efficiency inthe heat exchange unit 104 decreases, and the temperature of inksupplied to the head 50 tends to rise. Therefore, the controller 112controls the flow rate control valve 108 so that the flow rate of liquidmedium circulating in the heat exchange unit 104 increases. As a result,the heat exchange efficiency (heat exchange rate) in the heat exchangeunit 104 increases, the temperature of ink supplied to the head 50 islowered, and the ink temperature inside the head 50 gradually approachesthe reference value.

In the configuration example shown in FIG. 8, the revolution speedsensors 122 detecting the revolution speed of the pumps 102 are providedas a means for detecting the amount of ink supplied to the heads 50, butthis configuration is not limiting and a flow rate sensor detecting theflow rate (ink supply amount) in the ink supply paths from the liquidstorage unit 100 towards the heads 50 may be also provided. In thiscase, the controller 112 controls each flow rate control valve 108 so asto increase or decrease the heat exchange efficiency of each heatexchange unit 104 on the basis of ink amount detected by each flow ratesensor.

In the configuration example shown in FIG. 8, a table indicating therelationship between the revolution speed of the pump 102 and theopening ratio of the flow rate control valve 108 is maintained andfeedforward control is performed by which the opening ratio of the flowrate control valve 108 is changed according to the revolution speed ofthe pump 102.

FIG. 9 is a schematic diagram illustrating yet another configurationexample of an ink supply system according to the first embodiment. InFIG. 9, components common or analogous to those shown in FIG. 6 areassigned with like numeral symbols and explanation thereof is omitted.

In the configuration shown in FIG. 9, the print control unit 80 (seeFIG. 5) generates dot data from input image data, drives each head 50via the head driver 84 (not shown in FIG. 9) shown in FIG. 5, calculatesthe ejection ratio of each head 50, and sends the calculation results tothe controller 112. The controller 112 controls each flow rate controlvalve 108 on the basis of the ejection ratio of each head 50 receivedfrom the print control unit 80 (see FIG. 5).

For example, when the ejection ratio of the head 50 is low, then it iseasy to decrease the temperature of the head 50 since the drivefrequency is low, the heat exchange efficiency in the heat exchange unit104 is high since the supplied amount of ink supplied to the head 50 issmall, and therefore the temperature of ink supplied to the head 50tends to become low. Therefore, the controller 112 controls the flowrate control valve 108 so that the flow rate of liquid mediumcirculating in the heat exchange unit 104 decreases. As a result, theheat exchange efficiency in the heat exchange unit 104 is low, thetemperature of ink supplied to the head 50 rises, and the inktemperature inside the head 50 gradually approaches the reference value.

When the ejection ratio of the head 50 is high, the increase in drivefrequency easily rises the temperature of the head 50, the heat exchangeefficiency in the heat exchange unit 104 decreases since the suppliedamount of ink supplied to the head 50 is large, and therefore thetemperature of ink supplied to the head 50 tends to increase. Therefore,the controller 112 controls the flow rate control valve 108 so that theflow rate of liquid medium circulating in the heat exchange unit 104increases. As a result, the heat exchange efficiency in the heatexchange unit 104 increases, the temperature of ink supplied to the head50 decreases, and the ink temperature inside the head 50 graduallyapproaches the reference value.

In the configuration example shown in FIG. 9, a table indicating therelationship between the ejection ratio of the head 50 and the openingratio of the flow rate control valve 108 is maintained and feedforwardcontrol is performed by which the opening ratio of the flow rate controlvalve 108 is changed according to the ejection ratio of the head 50.

Further, in the present embodiment, a non-circulation system isdescribed in which the ink does not circulate between the liquid storageunit 100 and the head 50, but this configuration is not limiting and thepresent invention can be similarly applied to a circulation system inwhich the ink circulates between the liquid storage unit 100 and thehead 50.

Second Embodiment

FIG. 10 is a schematic diagram illustrating a configuration example ofan ink supply system according to a second embodiment. In FIG. 10,components common or analogous to those shown in FIG. 6 are assignedwith like numeral symbols and explanation thereof is omitted. Further,components outside the configuration between the liquid temperatureadjusting device 106 and the heat exchange units 104 (that is, theconfiguration between the liquid storage unit 100 and the heads 50) aresimilar to those of the configuration example shown in FIG. 6.Accordingly these components are not shown in FIG. 10.

As shown in FIG. 10, the ink supply system according to the secondembodiment is similar to that of the first embodiment in that the liquidtemperature adjusting device 106 and the heat exchange unit 104 arelinked by a supply flow path 114 and each of a plurality of firstbranched flow paths 116 which branch off from the supply flow path 114is provided with a flow rate adjusting device, but the configuration ofthe flow rate adjusting device in the second embodiment is differentfrom that in the first embodiment. Thus, in the first embodiment, theflow rate control valves 108 (see FIG. 6) are used, whereas in thesecond embodiment, electromagnetic valves 132 are used.

In the second embodiment, a plurality of flow paths (referred tohereinbelow as parallel flow paths) 130A, 130B, 130C are connected inparallel to each of the first branched flow paths 116, and theelectromagnetic valve 132 is provided in each of the parallel flow paths130A, 130B, 130C.

Part (some) or all of the parallel flow paths 130A, 130B, 130C may havedifferent flow path resistances, or all of the flow paths may have thesame resistance. In the former case, the adjustment range of thesupplied amount of liquid medium supplied to each heat exchange unit 104can be expanded. In the latter case, flow rate control of the liquidmedium in the heat exchange units 104 can be simplified because thesupplied amount of liquid medium supplied to the heat exchange unit 104is proportional to the number of parallel flow paths in which theelectromagnetic valve 132 is open, from among the parallel flow paths130A, 130B, 130C corresponding to this heat exchange unit 104.

In the configuration example shown in FIG. 10, the ratio of flow pathresistances of the parallel flow paths 130A, 130B, 130C is 1:2:4, andthe ratio of flow rates of liquid medium flowing in the parallel flowpaths 130A, 130B, 130C is 4:2:1.

In the configuration example shown in FIG. 10, three parallel flow paths130A, 130B, 130C are connected in parallel to each of the first branchedflow paths 116, but the number of parallel flow paths connected inparallel to the first branched flow paths 116 is not limited to thisnumber. Thus, two, or four or more parallel flow paths may be connectedin parallel.

Opening and closing of the electromagnetic valves 132 provided in theparallel flow paths 130A, 130B, 130C respectively is controlled by thecontroller 112. This control by the controller 112 is performed in thesame manner as in the first embodiment and explanation thereof is hereinomitted to avoid redundancy.

An example of control performed by the controller 112 will be explainedbelow. From among the electromagnetic valves 132 shown in FIG. 10, theelectromagnetic valves shown by white symbols are assumed to be in anopen state and those shown by black symbols are assumed to be in aclosed state. In this case, for example, as shown in FIG. 10, when theopening and closing of the electromagnetic valves 132 is controlled bythe controller 112, the ratio of supplied amounts of liquid mediumsupplied from the liquid temperature adjusting device 106 to the heatexchange units 104 is 5:7:4:5.

Thus, according to the second embodiment, by connecting in parallel aplurality of parallel flow paths 130A to 130C to the first branched flowpaths 116 connected to respective heat exchange units 104 andcontrolling together the opening and closing of electromagnetic valves132 installed in each of the parallel flow paths 130A to 130C, it ispossible to change individually the supply amounts of liquid mediumsupplied to the heat exchange units 104 and vary the heat exchange ratioof ink and liquid medium in the heat exchange units 104 with respect toeach heat exchange unit 104 (that is, with respect to each ink color).As a result, the temperature of ink supplied to the head 50corresponding to each color can be individually adjusted andinconveniences such as density unevenness caused by the difference inink temperature can be eliminated. Further, since electromagnetic valves132 that are less expensive and easier to control than the flow ratecontrol valve 108 (see FIG. 6) are used as the flow rate adjustingmeans, the cost of the ink supply system (ink supply device) of theinkjet recording apparatus 10 can be reduced.

Further, in the above-described embodiments, the liquid medium issupplied from one liquid temperature adjusting device 106 to a pluralityof heat exchange units 104. Therefore, when the supplied amount(circulating amount) of liquid medium to one heat exchange unit 104 ischanged by controlling the flow rate control valve 108 or theelectromagnetic valve 132, the supplied amount (circulating amount) ofliquid medium to another heat exchange unit 104 also changes. As aresult, the outlet temperature of ink flowing out of the other heatexchange unit 104 can be assumed to be changed.

Accordingly, the following relationship is valid between the ink inlettemperature (inlet temperature of ink flowing into the heat exchangeunit 104), ink outlet temperature (outlet temperature of ink flowing outof the heat exchange unit 104), and liquid medium temperature.

Ink Outlet Temperature=ε×(Liquid Medium Temperature)+(1−ε)×(Ink InletTemperature)  (1)

where ε is a temperature efficiency that can be represented asε=α×W^(1/2), α being a physical parameter of the heat exchange unit 104and W being a liquid medium flow rate (supplied amount of the liquidmedium supplied to the heat exchange unit 104). As indicated in Formula(1), as the liquid medium flow rate W changes, the ink outlettemperature also changes.

In a preferred mode of the above-described embodiments, when thecontroller 112 changes the supplied amount (circulating amount) ofliquid medium to one heat exchange unit 104 by controlling the flow ratecontrol valves 108 or the electromagnetic valves 132, the temperature ofliquid medium of the liquid temperature adjusting device 106 iscontrolled simultaneously. With such control, it is possible to maintaina constant ink outlet temperature of another heat exchange unit 104.

An example relating to two colors will be explained below.

When there is a difference in temperature between inks of two colors,the liquid medium flow rates W₁, W₂ are determined by the table in orderto obtain a constant ink outlet temperature. Further, temperatureefficiencies ε₁, ε₂ corresponding to the liquid medium flow rates W₁,W₂, respectively, are found from the formula ε=α×W^(1/2).

Where the ink outlet temperatures for two colors coincide in Formula(1), the following equation is valid.

ε₁×(Liquid Medium Temperature)+(1−ε₁)×(Ink Inlet Temperature1)=ε₂×(Liquid Medium Temperature)+(1−ε₂)×(Ink Inlet Temperature 2)  (2)

Therefore, the liquid medium temperature is determined from Formula (2).

Liquid supply apparatuses and image forming apparatuses in accordancewith the present invention are described in details above, but thepresent invention is not limited to the above-described examples and itgoes without saying that a variety of modifications or changes can bemade without departing from the essence of the present invention.

It should be understood that there is no intention to limit theinvention to the specific forms disclosed, but on the contrary, theinvention is to cover all modifications, alternate constructions andequivalents falling within the spirit and scope of the invention asexpressed in the appended claims.

1. A liquid supply apparatus comprising: a plurality of heat exchangedevices which are respectively provided in a plurality of supply pathsfor supplying liquids to a plurality of liquid ejection headsrespectively, are supplied with a liquid medium adjusted to apredetermined temperature from a liquid temperature adjusting device,and conduct heat exchange between the liquid medium supplied from theliquid temperature adjusting device and the liquids flowing in theplurality of supply paths; a plurality of flow rate adjusting deviceswhich are respectively provided correspondingly to the plurality of heatexchange devices and adjust a flow rate of the liquid medium supplied toeach of the plurality of heat exchange devices from the liquidtemperature adjusting device; and a controller which controls each ofthe plurality of flow rate adjusting devices to individually change theflow rate of the liquid medium supplied from the liquid temperatureadjusting device to the plurality of heat exchange devices.
 2. Theliquid supply apparatus as defined in claim 1, wherein: the plurality offlow rate adjusting devices are flow rate control valves; and thecontroller changes opening area of the flow rate control valves tochange the flow rate of the liquid medium supplied from the liquidtemperature adjusting device to the plurality of heat exchange devices.3. The liquid supply apparatus as defined in claim 1, wherein: each ofthe plurality of flow rate adjusting devices includes a plurality ofparallel flow paths in parallel connected in an individual flow path ofthe liquid medium to the heat exchange device, and a plurality ofelectromagnetic valves respectively provided in the plurality ofparallel flow paths; and the controller controls opening and closing ofthe plurality of electromagnetic valves to change the flow rate of theliquid medium supplied from the liquid temperature adjusting device tothe plurality of heat exchange devices.
 4. The liquid supply apparatusas defined in claim 3, wherein part or all of the plurality of parallelflow paths have mutually different flow path resistances.
 5. The liquidsupply apparatus as defined in claim 3, wherein all of the plurality ofparallel flow paths have a same flow path resistance.
 6. The liquidsupply apparatus as defined in claim 1, further comprising a pluralityof liquid temperature measuring devices which measure temperature of theliquids supplied to the plurality of liquid ejection heads respectively,wherein the controller controls each of the plurality of flow rateadjusting devices according to the temperature of the liquids measuredby the plurality of liquid temperature measuring devices.
 7. The liquidsupply apparatus as defined in claim 1, further comprising a pluralityof liquid flow rate measuring devices which measure flow rates of theliquids supplied to the plurality of liquid ejection heads respectively,wherein the controller controls each of the plurality of flow rateadjusting devices according to the flow rates of the liquids measured bythe plurality of liquid flow rate measuring devices.
 8. The liquidsupply apparatus as defined in claim 1, further comprising a headejection ratio calculation device which calculates ejection ratios ofthe plurality of liquid ejection heads, wherein the controller controlsthe plurality of flow rate adjusting devices according to the ejectionratios of the plurality of liquid ejection heads calculated by the headejection ratio calculation device.
 9. The liquid supply apparatus asdefined in claim 1, wherein the controller controls each of theplurality of flow rate adjusting devices and also controls temperatureof the liquid medium adjusted by the liquid temperature adjustingdevice.
 10. An image forming apparatus comprising the liquid supplyapparatus as defined in claim 1.